1. Field of the Invention
The invention relates to a technology for controlling a vehicle, and more particularly, to the technology for controlling the vehicle in correlation with the vehicle driving in front thereof.
2. Description of the Related Art
There has been a technology disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 64-69849, that is intended to support the safe driving for the driver by controlling various components of a vehicle running on the road (hereinafter referred to as a vehicle) in accordance with a distance (hereinafter referred to as a headway distance) between the vehicle and the vehicle driving in front thereof (hereinafter referred to as a preceding vehicle). In this technology, if the conditions, such as the headway distance that has been measured or the state where the vehicle is approaching the preceding vehicle, satisfy an appropriate predetermined condition, that is, the vehicle is fast approaching close to the preceding vehicle, the aforementioned technology executes a downshift of the transmission such that the braking force resulting from the engine brake is increased. In this case, the gear ratio of the transmission is controlled such that a target revolution is obtained by adding a coefficient (the difference in the revolutions between vehicles) to a reference revolution derived from an ordinary map.
The aforementioned conventional art controls the gear ratio of the transmission based on the uniquely established revolution irrespective of correlation between the vehicle and the preceding vehicle. Therefore, the resultant driving state of the vehicle is unstable, which may bother the driver of the vehicle by imparting an uncomfortable feeling, interfere with the driver with driving with the traffic flow, and have other unsatisfactory effects.